The present invention relates to electric transformers for transmitting electric power and more particularly to transformers one at least of the windings of which has integrated self-inductance.
Integrated self-inductance transformers are generally formed around a conventional magnetic circuit with two or three parallel columns connected together by two end crosspieces, the primary and secondary windings being coiled about the central column. The integrated self-inductance is obtained by providing an open auxiliary magnetic circuit surrounded by only one of the primary and secondary windings. The secondary magnetic circuit, unsaturable under normal conditions of use, limits for example the short circuit current of the transformer.
Such transformers with conventional magnetic circuit have in particular the drawback of being relatively bulky and heavy : the configuration of the magnetic circuit causes electromagnetic radiation harmful to the neighborhood of the transformer, which radiation is further increased very appreciably when a secondary magnetic core is incorporated for obtaining the self-inductance.
Electric transformers are further known, generally called toroidal transformers, whose magnetic core has a closed annular form. The primary and secondary windings of such a transformer are generally coiled one on the other. It is known that such a transformer is, for equal power, less bulky and less heavy than a conventional magnetic circuit transformer with two or three columns.
Such a toroidal transformer is however more difficult to construct, and in particular more difficult to wind, since the magnetic circuit is already closed during winding and the electric winding wire must pass as many times through the central chimney of the magnetic circuit as there are turns to form the coil.
Attempts have been made to construct toroidal transformers with integrated self-inductance, by separating the primary and secondary windings from each other, i.e. by coiling a first winding on a first circular sector of the magnetic circuit and coiling the other winding on a second circular sector of the magnetic circuit, different from the first sector.
Such a solution has not proved usable on an industrial scale, for it makes the electric windings even more difficult to coil on the torus and the coiling cannot be readily automated. Such an arrangement further leads to increasing the volumes, the copper sections forming the windings and the heating of the transformer; the self-inductance thus obtained is difficult to control quantitatively when it is desired to design a transformer having new characteristics. It has been further discovered that such a structure leads to increasing substantially the electromagnetic radiation in the vicinity of the transformer.